1. Field of the Invention
This invention relates to intake sound control apparatus especially for providing an even intake sound in an intake pipe of an internal combustion engine.
2. Description of the Prior Art
According to conventional apparatus, a muffler such as a resonator has been provided in the intake pipe for reducing intake noise in an internal combustion engine.
However, since the capacity of such a resonator is limited to a fixed value, an appropriate frequency for eliminating the noise is limited to a particular band. Accordingly, such apparatus does not select the a noise frequency which changes in response to engine speed.
Considering such problem, Toku-Kai-Sho (Laid open publication of Japanese Patent application) 59-3157 discloses an apparatus which includes a plurality of resonators, each of which has a different capacity, and a rotary valve which is provided in a common connecting passage for these resonators and which changes in response to the rotation speed of the engine.
However, according to this structure, there is another problem in that such apparatus needs too large of a space because of a number of resonators when put in a small room such as an engine room.
On the other hand, as a result of our enthusiastic research, it has been determined that noise frequencies having (n+0.5) harmonics of engine rotation speed as well as a noise frequency having a secondary component of engine rotation speed cause an unusual noise especially when the rotation speed is accelerated or decelerated, but that an even sound, which does not provide an uncomfortable feeling, can be obtained by eliminating noise having such frequencies.